In the process of industrial production, many harmful foams will be produced, and anti-foaming agents need to be added. There are many kinds of defoamer, organic siloxane, polyether, silicon and ether grafting, containing amine, imide and amide, with faster defoaming speed, longer foam suppression time, a wider range of applicable media, and even harsh media environments such as high temperature, strong acid and strong base characteristics. It is widely used to remove harmful foam produced in the production process of latex, textile sizing, food fermentation, biomedicine, coating, petrochemical, paper making, industrial cleaning and other industries.






1. Natural oils (i.e. soybean oil, corn oil, etc.)


Advantages: easy source, low price, simple to use;


Disadvantages: If the storage is not good, easy to deteriorate, so that the acid value increases.






2. High carbon alcohol


High carbon alcohols are linear molecules with strong hydrophobic and weak hydrophilic properties. They are effective antifoaming agents in water system. In the early 1970s, the former Soviet Union scholars tested in aqueous solutions of anionic, cationic and non-ionic surfactants, and proposed that the antifoaming effect of alcohol is related to its solubility and diffusion degree in the foaming solution. Alcohols of C7~C9 are the most effective antifoaming agents.


The high carbon alcohols of C12~C22 are prepared into water emulsion with particle size of 4~9μm and content of 20~50% with the help of appropriate emulsifier, which is the defoamer of water system.


There are also some esters, such as phenylethanol oleate, phenylacetate lauryl ester, etc., which has a defoaming effect in penicillin fermentation, and the latter can also be used as a precursor.






3, polyether defoamer


There are many kinds, mainly the following:


a. With glycerol as the starting agent, the GP type antifoam agent made of propylene oxide, or the mixture of ethylene oxide and propylene oxide by addition polymerization has poor hydrophilicity and small solubility in the foaming medium, so it is appropriate to use in thin fermentation solution. Its foaming inhibition ability is superior to the defoaming ability, and it is suitable to be added in the basic medium to inhibit the foam production in the whole fermentation process.


b. At the end of the polypropylene glycol chain, ethylene oxide is added to become a hydrophilic polyoxyethylene oxypropylene glycerol, also called. According to the ethylene oxide addition amount of 10%, 20%,...... 50%.


In this way, the defoamer has good hydrophilicity, easy to spread in the foaming medium, strong defoaming ability, but the solubility is also large, and the maintenance time of defoaming activity is short, so the effect is better in the viscous fermentation liquid.


c. A new polyether defoamer is a block copolymer with a hydrophobic stearate at the end of the defoamer chain to form a hydrophobic chain at both ends and a hydrophilic chain between them. The molecules of this structure are easy to gather horizontally at the gas-liquid interface, so the surface activity is strong and the defoaming efficiency is high.






4. Silicon


The most commonly used is polydimethylsiloxane, also known as dimethylsilicone oil. It has low surface energy, low surface tension, low solubility and high activity in water and general oil. Its main chain is the silicon oxygen bond, which is a non-polar molecule. It has no affinity with polar solvent water, and has little affinity with general oil. It is low volatile and chemically inert, relatively stable and less toxic. Pure polydimethylsiloxane can not be used as defoamer without dispersion treatment. It may be due to its high interfacial tension with water, low spreading coefficient, and it is not easy to disperse on the foaming medium. Therefore, the silicone oil is mixed with SiO2 aerosol, and the composite composed of SiO2 aerosol after hydrophobic treatment is mixed into dimethylsilicone oil, and it can be prepared after treatment at a certain temperature and for a certain time.


Silicone defoamer is made by mechanical emulsification of silicone grease, emulsifier, water repellent, thickener, etc., with appropriate amount of water. It is characterized by small surface tension, high surface activity, strong defoaming power, less dosage and low cost. It is not miscible with water and most organic matter, and can defoamer most bubble media. It has good thermal stability, can be used in a wide temperature range of 5℃-150℃, its chemical stability is good, difficult to react with other substances, as long as the configuration is appropriate, can be used in acid, alkali, salt solution, non-destructive product quality; It also has physiologically inert LD250g/Kg mice and is commonly used in the food and pharmaceutical industries. It has the function of suppressing and breaking bubbles for all bubble systems, and belongs to the category of broad-spectrum defoamer. It is widely used in detergents, paper making, pulp, sugar making, electroplating, fertilizer, additives, wastewater treatment and other production processes. In the petroleum industry, it is widely used in the desulfurization of natural gas to accelerate the separation of oil and gas. It is also used to control or suppress bubbles in the drying of ethylene glycol, extraction of aromatic hydrocarbons, processing of asphalt, dewaxing of lubricating oil, etc. In the textile industry, it is used in the process of dyeing, scouring, sizing and other defoaming; In the chemical industry, it is used for defoaming in the process of synthetic resin, latex, paint, ink, etc. In the food industry, it is used for defoaming in various concentration, fermentation and distillation processes. The silicone grease can be applied to the wall of the pot, the outlet or on the metal net for defoaming. The solution of silicone grease can be used for oil phase system defoaming. A water emulsion composed of silicone grease and low viscosity silicone oil can be used for defoaming of various water phase systems. In medicine, it is usually used to remove gas from the organs or stomach organs before surgery, X-rays, and gastroscopy.






5, polyether modified silicon


Combining the advantages of polyether and silicone defoamer, it is non-toxic and harmless, harmless to bacteria, and the addition amount is very small, so it is a cost-effective product.